Coded track circuit system of railway signaling



Aug. 22,1944. R M LAURENSON 2,356,460

coDED TRACK .CVIRCUIT SYSTEM 0F RAILWAY SIGNALING Filed Aug. 15, 1941 l 2l--22 1 Mg CH im# 16d l +]8:` /25 E 7375 2412 1g i EN 9i 9 i -L Patented Aug. 22, 1944 CODED TRACK CIRCUIT SYSTEM OF RAILWAY SIGNALING Robert M. Laurenson, Wilkinsburg,

Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application August 15, 1941, Serial No. 406,995

7 Claims.

My invention relates to railway signaling systems of the coded track circuit class, and it has special reference to automatic block and other systems of this character wherein provision is made for approach energizing wayside signals or other trafc governing devices.

Generally stated, the object of my invention is to provide new and improved facilities for approach controlling Various functions of coded track circuit signaling systems without the aid of line wires between signal locations.

A more specific object is to reduce the apparatus requirements and increase the utility of approach control facilities of the just defined nonline-wire class.

Another object is to make reset action by those facilities independent of the code following track relays at the entrance ends of the signaled sections. Y

An additional object is to prevent kick-back energy that may be generated in the section rails under shunted conditions thereof from falsely indicating that the circuited section is vacant while a train is still present therein.

A further object is to improve the operation of approach governed systems wherein coded direct current energy for wayside signal control is at times supplemented by coded alternating energy for cab signal control.

In practicing my invention, I attain the above and other objects and advantages by organizing the elements of each coded track circuit combination in a novel and improved manner. In my new organization, pick-up current for the entrance end track relay is supplied from an entrance end source; the code following releases of that relay needed for signal indication selection are produced by neutralizing pulses of signal code energy supplied from an exit end source; an exit end train detector relay normally receives energizing pulses from the entrance end source during the signal code olf periods; and the normally deenergized approach governed devices are rendered active when and only when transmission of those detector relay energizing pulses becomes discontinued by a shunting of the circuited section rails.

I shall describe several track circuit combinations embodying my invention and shall then point out the novel features thereof in claims. These illustrative embodiments are disclosed in the accompanying drawing in which:

Fig. 1 is a diagrammatic representation. of a section of railway track which is equipped with one preferred form of the approach control facilities of my invention;

Fig. 2 indicates the different forms of energy which are eective in the track circuit of Fig. 1 during vacant conditions thereof;

Fig. 3 is a diagrammatic showing of the approach governing facilities of my invention applied to a track circuit combination wherein coded direct current energy for wayside signal control is at times supplemented by coded alternating current energy for cab signal control; and

Fig. 4 shows how the polar biased trackrelay of each of the Fig. 1 and Fig; 3 track circuit combinations may be replaced by a track relay of the polar stick type.

In the several views of the drawing, like reference characters designate corresponding parts. Referring rst to Fig. 1, the improved approach control facilities of my invention are there disclosed in association with a coded track circuit system of automatic block signaling for a railway track l-2 over which it will be assumed that traffic moves in the single direction indicated by the arrow, or from left to right in the diagram. The protected stretch of this track is divided into the customary successive sections by insulated rail joints 3 and the rails of each section form a part of a new and improved track circuit combination which will be described presently. f

In this view of Fig. 1, reference characters D and E respectively designate the entrance and the exit ends of one of these track sections; character TR designates a code following track relay which is installed at the entrance end of the section; character TB a track battery or other direct current source provided at the section exit; character CR a coding device having a contact 5 which periodically connects this track battery in energy supplying relation with the section rails; and character S the usual wayside signal which guards the entrance of each of the track sections and which is controlled by the associated track relay TR through the medium of decoding apparatus DA.

An automatic block signaling system of the referred to code track circuit type operates without the aid of line wires and, in representative form, it includes all of the elements above named. Such a system further comprises the customary facilities (not shown) for continuously operating each of the exit end relays CR at one or another of the usual plurality of distinctive code rates. Selection among these rates (which in a typical three indication system may consist of and and R in the typical three indication system above referred to) of the wayside signal at the same location. In the arrangement representedT n these signal lamps derive energizing current'from a power source which is designated by the terminals plus and minus In order that certain functions of the signaling system may be rendered active` only upon the approach of a train, the apparatus installed at each of the signal locations D, E, and so forth', is.

supplemented by a train .detector relay KR which Y is arranged to maintain the referred to'funcf tions inactive at all times except when theY section of track to the rear ofthe location becomes occupied. In the illustrative arrangement of Fig. l, only one such approach control function has been provided for andit consists in lighting the wayside signal Se (normally dark) over a contact 9y of the detector relay KR.

When applied to block signaling systemsV of the frequency code character here considered, the improved track circuit facilities of myY invention render the relay KR at each .signalJ location responsive to the approach of a train and they do this, moreover, withouttheuse of control line wire between signal locations. Embraced by such facilities are track circuit'elements organized in the novel manner. which will now be described..

The novel track circuit combinati'11l ofliyv.

Serving to operate the code following and detector track relays TR and KR at the section entrance and exit ends is a track circuit combination of new and improved character; In it, pick-up current for the entrance end track relay TR is supplied from an entrance end source of directcurrent shown in the form of a trackbattery KB; the code following releases of that relay which are needed for signal indication selection are produced by neutralizing pulses of signal code energy that are supplied from the exit end source TB over the back point of coding contact the exit end train detector relay KR receives pulses of entrance source energy over the front point of contact 5 during the signal code off periods; and the normally deenergized wayside signal Se receives lighting current over back contactS when and only when transmission of those detector relay energizing pulses becomes discontinued by the shunting of section D-Es rails.

Examining entrance location Ds apparatus in greater detail it will be seen that the direct current source KB is continuously connected across the section rails through a circuit which includes an impedance l2. By this connection there is 'established between the rails a difference of potential having the positive or` given polarity character represented by the KB potential portion of Fig. '2.

Thev entranceend track relay TR is bridged across these rails, through the usual impedance liiand hence has impressed thereon the voltage of source KB reduced only by the potential drops whichv occur in impedances l2 and I3. In the trance end direct current source KB and also with those for the section rails l-2 at the entrance location D. Relay TR is, in consequence, normally held picked up by the given polarity potential -from the source KB.

Examining next the apparatus at the exit end location E, it will be seen that the direct currentsource .TB thereat is by coding contact 5 of device CR connected with the section rails in such manner as to supply them with energy which makes rail 2 positive with respect Atorail l. This energy polarity directly opposes that of the entrance end sourceKB and reacts thereon in a manner to be described presently.

In periodically operating as aforesaid, coding device CRs contact 5 thus Iconnects theI exit end source TB with the section rails in a manner to supply them with on 'period pulses of opposing polarity energy that are separatedby orf period intervals. This pulsed signal control energy is passed through the usual current limiting impedance I5 and it has the recurring cycle character which the TB-CR code portion of Fig. 2 represents.

As earlier mentioned, the exit and detector relay KR is connected with the, section rails during and only during the oif periods of the just described signal control code. Producing this recurrent connection is the coding contact 5 (front point) and included therein is an impedance I6.

For a purpose later to be made evident the relay KR is sufficiently slowl releasing to bridge the on code periods by which the just named off period connections are separated. For producing this release delay use may, of course, be made of anyy suitable means such as a snubbing impedance (not shown) bridged across the winding terminals or internal design expedients incorporated in the relay.

Operation of the Fig. .1 combination Under the represented vacant conditions of section DE, the entrance end track relay TR recurrently picks up and releases in step with the code 'following operation of the exit end coder device CR. Unlike conventional systems, however, each on period of signal code energy from exit end source TB is accompanied by a release of track relay TR and each off period of the same code is accompanied by a pick-up of the track relay.

The reason for this will become more evident upon reference to Fig. 2. Diagrammed by the upper portion thereof is the positive or given polarity potential which entrance source KB impresses upon the section rails; diagrammed by the TB--CR code portion is the pulsed negative or opposite polarity potential which kthe rails receive from the eXit end signal code apparatus; and diagrammed by the lower portion is the resultant trackway .potential which becomes effective for energizing the entrance end track relay TR and also the exit end detector relay KR.

Energy is supplied from battery KB through resistor I2 to two branch circuits in multiple.V One of these branch circuits includes in series therewith the winding of track relay TR and the resistor I3. The other or second branch circuit includes in seriesjtherewithA the track rails and equipment at the exit end of the section. When contact 5 of coding relay CR is picked up the winding of relay KR is `connected across the' section rails in series with resistor I 6, and is therefore included in lseries with the second branch circuit to which energy is supplied from battery KB. The various elements ofthe track circuit apparatus are arranged' and proportioned so that under the most adverse ballast conditions suiicientjenergy issupplied `to both relays TR and-KR to pick up their contacts.

On movement of the contact 5 of relay CR to its released position, the relay KR is 'disconnected from the section rails, while the battery TB is connected across the section rails in series with resistor I5. Accordingly, the battery 'I'B is now connected in the second branch circuit referred to above. The battery -TB and resistor I5 may be of lower resistance than the winding of relay KR and resistance I6, and when the battery TB and resistance I5 are substituted for relay KR and resistance I6 in the second branch circuit identied above, there is an increase in flow of energy from the battery KB in this branch circuit and an accompanying decrease in the flow of energy from the battery KB to the other branch circuit, that is the branch circuit which includes the winding of track relay TR.

` In addition, when battery 'I'B is connected lacross the track rails energy is supplied therefrom over the track rails to the entrance end of the track section, where this energy divides between two branch circuits. One of these branch circuits includes in series therewith the resistor I3 and the winding of track relay TR, while the other branch path includes in series therewith resistor I2 and battery KB. The battery 'I'B is included in the circuit in such manner that the energy supplied therefrom to relay TR flows through the winding of relay TR inthe opposite direction to the energy supplied from battery KB to the section rails. The various elements of the combination are arranged and proportioned so that the energy supplied Yfrom battery TB to relay TR suiciently offsets that supplied from battery VKB to effect release of the relay contacts.

On subsequent. movement of contact 5 of relay CR to its Ypicked-up position, thebattery TB f ceases to be connected across the section rails, while relay KR is again connected across the section rails. Accordingly, energy is no longer supplied from battery TB to relay TR, while energy from battery ICB is again supplied to relays 'I'R and KR and the contacts of relay 'I'R pick up, and the contacts of relay KR remain picked up.

Accordingly, on continued code following operation of the relay CR, energy from the battery KB picks up the track relay TR and energizes the relay KR during the picked-up periods of contact 5, while during the released periods of contact 5 energy from battery I'B feeds to relay 'IR and causes its contacts to release.

Whereas, however, relay TR follows code, the

exit detector relay KR remains continuously picked up under these vacant section conditions. As earlier stated, this continuous pick-up is due to relay KR having sunicient'krelease delay to rent energizing pulses are separated. Y y

Nor dochanges in frequency ,of signal control code pulse recurrence alter the action just eX- plained. Operation of the 'complete signaling system of which the Fig. l track circuit` forms apart involves, of course, such changes.`r In the three kindication organization earlier referred to clear and approach codes of and 75 cycles per minute are typical.

For either of these code speeds (and also duringothers which the system may utilize) my improved trackcircuit combination is found-to operate in the desired' manner earlier described, wherein the entrance trackrelay TR follows code at a ratewhich determines the signal indication and lthe exit end detector relay KR holds contact 9 continuously picked'up. Because of that picked up condition the approach governed signal 4'Se is normally maintained inactive. i Upon entry of a train into section D-E the accompanying shunt of the section rails removes energizing current from both the entrance `relay IR and the exit relay'KR. In now releasing, the latter device completes over its contact 9 the lighting Vcircuit for wayside signal'Se and thereby causes that signal to display to the train the indication ywhich advance traiiic conditions determine. Such display, quite obviously, continues as long as any part of the train remains in the section D-E.

' Upon departure of the train from the section the'resulting vshunt removal allows the positive or given polarity potential from entrance source KB vagain to appear between the rails and also allows the on period pulses of opposite polarity signal control energy to be transmitted thereover from theV section exit. The train departure is, in consequence, accompanied by an immediate pick-up of entrance lrelayTR and restoration of that relay to its vnormal code following condition. Further accompanying that departure is a prompt reception by exit detector relay KR of off period pulses' of pick-up energy from'entrance source KB. By those pulses relay KR. is held picked up and contact 9 thereof now restores approach controlled signal Se to its normally inactive state. It is/tolbe noted that the just described response of detector relay KR to the train departure is completely independent of the entrance end track -relay TR land-'even'were device TR to be removed from the combination the response would take place in the manner intended. This isz'because of the Hcontinuous connection of entrancevso-urce KB across the'secti'on rails and the direct availability of this'potential kfor picking up relay KR onceV the section rails'become unshunted.

In addition'to the obvious advantage of absolute reliability, the just explained characteristic reduces the apparatus requirement of non-linewire approach control facilities for coded track circuits,. Past commercial provisions of such facilities are typified by the coded feed back organization which is disclosed and claimed by Herman G. Blosser Reissue Patent No. 21,783. AIn the track circuit combination of that patent, use is made of an impulse relay IR (not here shown) which is required at the section entrance end to transfer the rail connection from the track relay TR to thefeed back source AB corresponding to source KB hereof) during each olf period of the receivedsignal control code. By eliminating the needfor such an impulse relay, the

bridge the"on code periods'by which its recurboth instances and improved combination yof my inventioneffects important savings in'track circuit apparatus. f -The tmckcircuit organization of Fig. A3

Consideration of the polarities whichare necessary to make the' Fig.v 1 track circuitoperable. shows that they have the opposing entrance and exit source relations earlier pointed out in de.- tail. This is the desirable polarity from the standpoint of safeguarding the` eXit detector relay KR from false operation in the event of an accidental bridging of the front and back` points of coder relay CRs Contact 5.

' It is', however, undesirable from the standpoint of safeguarding the detector relay KR from false operation dueto inductive kick-back energy which may be generated in the rails l-Z of thel direct current track circuit'D-E when those rails are Vshunted by a train; When sogenerated this energy appears in the rails at the end of each on period pulse of the unidirectional current with which source TB supplies the trackway over the back point of coding contact 5. Direct current track circuits employing detector relays of the type shown at KR can experience serious operating difficulties due to suchkickback energy and one early proposal to overcome such diiculties forms the subject of assignees Patent 2,286,002, which issued to Frank H. Nicholson on June 9, 1942.

As the speciiication of that patent sets forth in considerable detail, kick-back energy ofthe type here considered'results fromthe inductance of the track circuit plusV the conductance of the rail-to-rail ballast and its effect is to continue for a short interval after each disconnection of direct current source TB from the section rails the flow of current in those rails in the same direction as was established Icy-source TB.

Hence, when the rails of Fig.- ls section D-E are shunted by a train each on period pulse of traokway current which source TB impresses upon those rails thus may be followed by a kickback energy pulse which though relatively short still is of sufficient duration to overlap the early portion of the succeeding o code period. Current due to these overlapping pulses thus may reach relay KR over the front point yof coding contact 5 and if of sunicient magnitude such oif'period current may falsely pick up relay KRv even though the signal Se approach controlled thereby should stay lighted until the train has cleared the section.

In order to reduce the Vpossibility of thistrou- Y ble' and provide additional simplification, the circuit shown in Fig. 3 may be utilized. In its basic organization it duplicates the earlier described combination of Fig. 1. Thus, the entrance end portions at location D are exactly the same in the exit end portions at location E diier only in that: 1) the train detector track relay has the form of a code following device KRI; (2) the approach lighting contact 9 is carried by a slow release repeater AR which derives pick-up current over a contact I8 of relay KRI; (3) the circuit over which source TB supplies direct current to the track rails includes acontact I9 of relay AR; and (4) provision is made for at times supplying the section rails with coded alternating energy for cab signal control.

This provision is shown as taking the form of a track transformer TT having a secondary Winding connectable with the rail supply circuit over the back point of contact I9 and having a primary winding which-is connected with'a sourcev B-C of cycle per second-or other-`V commercial carrier Wave frequency` alternatingcurrent energy.

These alternating current energy supply facilitiesL will, quite obviously, be provided only when the signaled track is to carry vehicles which *are equipped with cab signaling equipment and insofar as the kick-back energy is concerned, they either may or may not be used. Further consideration'thereof will, accordingly, be reserved for a later part of this description.`

In its broader aspects the supplemented track circuit combination of Fig.'3 duplicates the operation of the Fig. 1 combinationV That is, vacant conditions of the circuited section D-E are accompanied bya code following action of entrance track relay TR and off period energizations of the exit detector relay KRL Instead, however, of staying continuously picked up as does device KR of Fig. 1, relay KR!v of Fig. 3 picks up and releases itscontact I8 in step with the off and the on periods of the direct current signal control code that results from contact 55s recurrent connection of exit source TB with the section rails. I

The repeater or approach relay ARis, in consequence, recurrently energized from the local source p1usminus and, due to its slow releasingA characteristics, it holds contacts S and I9 continuously picked up. This insures the desired deenergization of the approach control signal Scand also keeps the direct current'source TB included in the rail supply circuit.

Entry of a train into Fig. 3s section D-E, deenergizes and hence continuously releases both the entrance track relay TR and the exit detec-l tor relay KRI. By the latter release, approach relay AR becomes continuously deenergized and hence drops contacts .Q -I9. That actionr causes lighting current to be supplied to signal Se and also removes (at contactv I9) the direct current source TB from the rail supply circuit of which coding contactV 5 forms a part.

By that removal, all coded direct current energyis prevented from reaching the section rails and all possibility of kick-back energy generation is thereby removed. The kick-back energy thus having been eliminated, the detector relay KRI is no longer subject to false energization under occupied conditions of the rear- Wardly vextending section and the problem earlier discussed is thereby fully and satisfactorily solved. Nor does thissolution in any way interfere with other operating characteristics of the supplemented track circuit. As long as the circuited section remains occupied there is no necessity for any supply of coded direct current energy thereto, and when the train clears the sections eXit end E this supplyof direct current coded energy is promptly restored to the rails.

Such restoration results, in the organization of Fig. 3, from the flow of entrance end energy from source KB to the winding of detector relay KRI over the now unshunted rails and the front point of exit contact 5. By that flow, contact I8 is picked upto energize'the repeater relay AR and cause its contact IS to reinsertthe direct current source TB into the rail supply cir? cuit.

Such reinsertion, quite obviously, occurs very quickly and thus assures that each clearance of the circuited section will promptly be followed by a pick-up of contact i9 and an attendant restoration of coded direct current energy to the section rails.

Once so restored the "on period pulses of sig,- nal control energy produce code following operation on the part of entrance track relay TR and thereby continues the track circuit combination in its normal or vacant section condition until another train comes into the section. In the p articular organization of Fig. 3, each of the named on period pulses is impressed upon the section rails by Way of a circuit extending fromY the positive terminal of direct current source TB through conductor 2|, track railsI and 2, conductor 22, back contact 5 of device CR, conductor 23, front contact I9 of device AR and impedance I 5 back to the negative terminal of source TB.

Because of the continuous connection of the entrance source KB with the section rails, the code reproduction by the detector relay KRI is completely independent of relay TR and it is because of this characteristic that removal of all coded direct current energy is possilbe under occupied conditions of the section.

As shown in Fig. 3, contact I9 by which this removal is eiected is carried by a slow release approach relay AR. The same results may, quite obviously, be achieved by making the detector relay KRI a slow acting device, as in Fig. 1 (relay KR thereof), and placing contact I9 directly thereon. With such a combination, each entry of a train into the circuited section again releases contact I9 and thereby removes the direct current source TB from the rail energizing circuit. Such removal continues until the section is cleared by the train at which time relay KR,

receives pick-up current from entrance source KB and directly causes contact I9 to reinsert source TB into the coding supply circuit of which contact 5 forms part.

Returning now to the cab signal supply elements B-C and TT of Fig. 3, these are inactive under all Vacant conditions of section D-E and are so continued by the normally picked up contact I9 of device AR. When, however, the sec- `tion becomes occupied by a train, the resulting `release of contact I9 first moves direct current source TB from the rail supply circuit and then Aincludes the secondary of transformer. TT

therein.

Under conditions of such inclusion, each movement of device CRs contact 5 to its lowermost position causes the section railsto be supplied with a pulse of alternating current energy from source B-C. The circuit over which this supply takes place may be traced from the righthand terminal of transformer TTs secondary through back contact I9 of device AR., conductor 23, back contact 5 of device CR, conductor 22, track rails I and 2 and conductor 2I back to the left terminal of the TT transformer secondary.

The resulting coded alternating current energy has the same suitability for controlling train carried cab signals as were it to be supplied over exit end circuits of conventionalcharacter. The frequency of its pulse recurrence is, quite obviously, dependent upon the rate which coding relay CR operates contact 5, andV that rate, as already pointed out, is determined by conditions of traflic in advance of the supply location E.

Once instituted, moreover, the coded alternating current supply continues until the rearwardly extending section D-E becomes cleared by the train. When that happens, relay ARs contact I9 picks up and. in s o doing it removes `form of a polar stick device TRI.

the transformer TT from the rail supply circuit vand reinserts the direct current source TB therein. As long as the section remains vacant, coded direct current and only direct current energy is supplied to its rails. Y

The just described separation of the direct current trackway energy from Vthe alternating current cab signal energy by contact I9 ofthe train detector repeater is made possible by my earlier disclosed novel combination of the detector track relay KR with the entrance end source KB that is continuously connected across the section rails. As tests in the field have indicated that the major portion of the earlier mention kick-back energy is due to direct current code pulses, the named separation results in a substantial reduction in the kick-back effect that is present in combination Where coded direct current for wayside signalcontrol is at times supplemented by coded alternating current energy for cab signal control.

Further desirable results also accrue from the named separation. Tests on a 6000 foot track circuit show that about 15 or 20% of the required cycle cab signal energy is expanded in a track limiting resistor of the characterV shown at I5 when such a resistor is included, as has been necessary in the past, in the cab signal supply circuit. Fig. 3s elimination of that resistor from the circuit thereforeeiects marked economies in cab signal power requirements and it also saves Vwear and tear on y conventional tuned alternators (not shown) when such are used to provide the 100 cycle alternating current from direct current sources of the track or control battery type. A g

Since, moreover, the named separation removes all short circuit drain from the vtrack battery TB, the wear on coding device CRs contact 5 is substantially reduced. Still further, the separation function can be performed without requiring additional contacts on the approach relay AR of conventional exit end combinations of approach control alppafratus. In such conventional combinations, acontact is customarily used to short circuit the track transformer TT under vacant conditions of the rea wardly extending section. With the improved arrangement shown in Fig. 3, such` short circuiting no longer becomes necessary and the contacts which ordinarily would perform it may therefore become available for use as element I9.

Polar stick track relay of Fig. 4'

track relays of the neutral or non-polar type will operate satisfactorily in each of the track circuit combinations of Figs. 1 and 3.

Still further types of code following track relays also are usable in those combinations and one of these is shown by Fig. 4 as taking the vSuch aY device has contacts (see element 30) whichoccupy the left or norma position when and after positive or normal polarity Vpotential isapplied of Fig. 2 has the completely balto the relay Winding and which occupy the right or reversed position when and after the relay winding receives negative or reversed polarity potential. To shift these contacts from one position to the other the potential applied to the relay winding must not only be reduced to zero but it must also be built up in the opposing polarity direction.

Assume now that the polar biased track relay TR of Fig. 1 is replaced by the polar stick track relay TRI of Fig. 4. The normal polarity potential from entrance source KB will, quite obviously, hold relay TRIs contact 30 in the left or normal position. That positioning will continue, moreover, until opposing polarity potential is applied to the relay winding.

In the particular energy relations which Fig. 2 shows, such opposing polarity application will not, however, take place for the reason that each on period pulse of TB-CR. code potential from opposing polarity source TB merely neutralizes the normal potential from source KB but does not provide any opposing polarity eX- cess for track relay energization.

If, however, the voltage of source TB be raised (or if certain other track circuit adjustments be made), then an excess of opposite polarity potential will appear at entrance location D during the on code periods and track relay TRI will by that excess potential have its contacts shifted to the right or reverse position during each of those on periods.

Under those conditions polar stick track relay TRI will follow code in the desired manner and its contacts then can be used to operate decoding apparatus D-A in the same way as do those of polar biased track relay TR. That track relay TR of Fig. 1 can, therefore, be replaced by the polar stick track relay TRI of Fig. 4 without interfering with the basic operation of the Fig. 1 track circuit combination.

As will now be evident, a similar substitution may be made in the Fig. 3 combination-if the energy-supply elements thereof be so adjusted that each on period pulse of opposing polarity energy from source TB not only overcomes the normal polarity potential from source KB but also provides an excess of opposing polarity potential for track relay energization.

Summary Regardless of the type of track relay used, the herein disclosed circuit organizations of Figs. 1 and 3 both eliminate the necessity for an entrance end impulse relay of the character shown at IR in the Blosser Reissue Patent No. 21,783 plus that relays transformer energizing facilities. Both further eliminate the time lost in picking up such an impulse relay during each off period of the received signal control code.

This latter elimination assures that the pulses of entrance end energy which reach the exit end detector relay KR will be of the full off period length instead of being of the relatively short character shown at lc in Fig. 3 of Edward U. Thomas Patent No. 2,172,893. Because of this lengthening, all need for the detector relay stick circuits of the Thomas patent type is eliminated and code following detector relays may, therefore, take the simplified form shown at KRI in Fig. 3 of the present application. i

Such elimination, furthermore, means that in a repeater relay combination of the type shown in Fig. 3 the slow release device KR may `effectively be energized over a simple circuit ofthe "asta/ico direct controlled type shown. Since relay KRI has substantially equal pick-up and release times, the limitations on the minimum release delay of the repeater AR are widened. That relay can, therefore, be designed to `consume less `energy and-be made with a shorter release time which will improve block joint shunting response. Furthermore, it can be operatedfrom the conventional line battery, if desirable.

Whileit is true that some of the foregoing advantages are obtained at the expense of a somewhat increased track battery drain, .the effective local energization of the entrance end track relay TR gives some compensation for this added drain, as does also the elimination 0f the requirement for a stick circuit on exit end detector relays of the code following type shown at KRI in Fig. 3.

While I have explained my invention in appli.- cationswherein the lights of wayside signals (Fig. 1 and Fig. 3) and the cab signal control energy supply only are approach controlled, it will be understood that it hasequal utility when used with approach control combinations which provide for other comparable functions insteadof or in addition to the illustrative ones just named. One such further function might consist vin operating highway crossing signals (not here shown) or the like; a second -in the approach lighting of station platform lights; and a third in the locking of track switches at Crossovers in automatic territory.

From the foregoing it' will accordinglyfbe seen that I have made substantial improvements in the art of approach vcontrolling railway signaling systems of the coded track circuit class. More specically: (1) I have reduced the apparatus requirements and increased the utility of approach control facilities of the non-line-wire coded system class; (2) I have made reset action by those facilities independent of the vcode following track relays at the entrance end of the signaled section; (3) I have prevented ,kickback energy that may be generated in the section rails under shunted conditions thereof from falsely indicating that the circuited section is vacant while a train is still. present therein; and (4) I have improved the operationof approach governed systems wherein coded direct current energy Vfor wayside signal control is at times supplemented by coded alternating current energy for cab signal control.

Although I have herein shown and described only two forms of approach control combinations embodying my invention,l it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit andscope of my invention.

Having thus describedV my invention, what I claim is: y

1. In a coded railway signaling system, in combination, a section of railwaytrack through which trac normally moves Yin a givenV direction, a track relay at the entrance end of said track section having its winding connected across the section rails, an approach relay and a iirst'battery located at the exit end of the track section, a coding device having a contactcontinuously actuated between a first position and a second position, means for connecting said approach relay across the section rails when said coding device contact is in its first position, means for connecting said rst battery across the section rails when said coding device contact is in its second posi- '2,356,460 tion, and a second battery locatedl at the entrance end of said track section, said second battery being connected across the section rails in multiple with said track relay and being arranged to supply to said track relay energy of a polarity and of a value effective to cause the track relay contacts to move from their rst to their second positions and to also supply to the track rails energy which when supplied to the approach relay is effective to operate said relay, said :first battery being effective when connected across the section rails to supply to said track relayk energy of a polarity opposite to that supplied to said track relay from said second battery and of a value effective to cause movement of the track relay contacts from their second to their rst positions.

2. In a coded railway signaling system, in combination, a section of railway track through which traffic normally moves in a given direction, a code following track relay at the entrance end of said track section having its winding connected across the section rails in series with a rst resistor, a rst battery located at the entrance end of said track section, said first battery being connected through a second resistor to a rst branch circuit including in series therewith said rst resistor and the winding of said track relay and to a second branch circuit including the section rails in series therewith, an approach relay and a second battery located at the exit end of the track section, a coding device having a contact which is continuously actuated between a first and a second position, means for connecting said approach relay across the section rails when said coding device contact is in its first position, and means for connecting said second battery across the section rails when said coding device contact is in its second position, the elements of the combination being arranged and proportioned so that when the section is vacant and the coding device contact connects the approach relay across the section rails energy is supplied from said rst battery over said section rails and operates said approach relay and is also supplied from said first battery to the track relay and flows through the track relay winding in a given direction and causes the track relay contacts to move from their rst to their second position, the elements of the combination also being arranged and proportioned so that when the section is Vacant and the coding device contact connects said second battery across the section rails energy is supplied from said second battery over the section rails and iiows through the winding of the track relay in f the reverse of said given direction and causes the track relay contacts to move from their second to their rst position.

3. In a coded railway signaling system, in combination, a section of railway track having a first and a second track rail over which trailc normally moves in a given direction, a code following track relay located at the entrance end of said section, the winding of said track relay being connected across the section rails in series with a first resistor with the first terminal of said winding connected to the first track rail, said track relay having a contact which when in its rst position is moved to its second position when and only when energy flows through the relay winding from its rst to its second terminal, a first battery located at the entrance end of said section, said battery being connected through a second resistor across the track rails and also across the terminals of the track relay winding in series with said rst resistor, the positive terminal of said rst battery being connected to the first terminal of the track relay winding, an approach relay and a second battery located at the exit end of said section, a coding device having a contact continuously actuated between a first and a second position, means for connecting said approach relay across the section rails when said coding device contact is in its first position, and means effective when said coding device contact is in its second position to connect said second battery across 'the section rails with the positive terminal of said battery connected to said second track rail so that energy supplied from said second battery to the track vrelay winding flows through said winding from its second to its rst terminal, the elements of the combination being proportioned so that when the section is vacant and the coding device contact connects the approach relay across the section rails energy from the rst battery operates the approach relay and causes the contacts of the track relay to move from their rst to their second position, and so that when the section is vacant and said coding device contact connects the second battery across the section rails energy from the second battery is supplied over the section rails to the winding of the track relay and causes the contacts of the track relay to move from their second to their rst position.

4. In a coded railway signaling system, in combination, a section of railway track having a rst and a second track rail over which traffic normally moves in a given direction, a code following track relay having a contact biased to a released position and movable therefrom to a picked-up position when and only when energy flows through the relay winding from its first to its second terminal, the winding of said track relay being connected across the section rails in series with a first resistor with the rst terminal of said winding connected to the first track rail, a rst battery located at the entrance end of said track section, said first battery being connected through a second resistor across the track rails and also across the terminals of the track relay winding in series with said first resistor, the positive terminal of said battery being connected to the first terminal of said track relay winding, anapproach relay and a second battery located at the exit end of said section, a coding device having a contact continuously actuated between a rst and a second position, means for connecting said approach relay across the section rails when said coding device contact is in its first position, and means effective when said coding device contact is in its second position to connect said second battery across the section rails with the positive terminal of said battery connected to said second track rail so that energy supplied from said second battery to the track relay winding flows through said winding from its second lto its first terminal, the elements of the combination being proportioned so that when the section is vacant and the coding device contact connects the approach relay across the section rails energy from the first battery operates the approach relay and causes the contacts of the track relay to pick up and so that when the section is vacant and said coding device contact connects the second battery across the section rails energy from the second battery is supplied over the section rails to the winding of the track relay and causes the contacts of the track relay to move from their picked-up to their released positions.

5. In a coded track circuit signaling system for railroads, a code transmitting and receiving =means comprising a code following detector relay,

a slow releasing relay governedby said detector relay, a track battery, and a Acoding device having a contact continuously actuated between a-vrst vposition in which it establishesa circuit including a slow releasing relay governed by said detector relay, a track battery, a track transformer, and a coding device having a contact continuously actuated between a rst and a second position, said coding device contact being effective when in its rst posit-ion to establish a circuit lto connect said track battery or the secondary winding of said track transformer across the rails of a section of railway track according as the contacts of said slow releasing relay are picked up or released, said coding device Contact being eiective when in its second position to connect the winding of said detector relayacross said rails.

7. In a coded track circuit signaling system, a code transmitting and receiving means comprising acode following detector relay, a slow releasing relay governed by/said detector relay and having contacts which are picked up when and only when said detector relay is responding to energy supplied over the rails of a track section, and a coding device having a contact continuously actuated between a irst and a second position, said .codingdevice contact being eiective when in its rst position provided the contacts of said slow releasing relay are picked up to connect a source of current across the rails of a track section and being effective when in its second position to ccnnect the Vwinding of said detector relay across said rails.

ROBERT M. LAURENSON. 

